The present invention relates to a method for the pneumatic transportation of a particulate material at controlled rate or, more particularly, to a method for the pneumatic transportation of a particulate material in which, when an external disturbance is added to the transportation system, the external disturbance is rapidly absorbed to maintain the acting capacity of the transportation system at a preset level or, when the preset level of the transportation rate is changed, the desired new transportation rate can rapidly be established with self-correctability of the transportation capacity in compliance with the changes in the properties of the particulate material under transportation.
In a conventional pneumatic transportation system of a particulate material, as is illustrated in FIG. 5 of the accompanying drawing, presetting of the desired transportation rate Ws is followed by the setting of the flow rate Qb of the booster gas and the pressure Pt in the pressure tank determined by the preliminary calibration running before the actual operation of the system. The actual transportation rate WA of the particulate material under transportation is measured as a differential value of the output signal from the weighing instrument of the pressure tank and/or by means of a flow meter for a particulate material installed on the way of the transportation piping. The flow rate Qb of the booster gas is controlled by means of a flow rate controller installed on the way of the supply line of the booster gas in accordance with the deviation of the actual transpotation rate WA from the preset value Ws of the desired transportation rate so as to maintain the transportation rate W of the particulate material at the preset level Ws.
When the transportation system under the above described control means receives certain external disturbance such as fluctuation of the pressure Pb in the receiving unit or the pressure Pt in the pressure tank and presence of a foreign body in the transportation piping, a considerable length of time lag is unavoidable before the conversion of the actual transportation rate WA of the particulate material to the preset value Ws of the desired transportation rate even by providing each of the detectors and controllers with the highest sensitivity because the controlling movement of the controller is started only after the detection of the increment or decrement in the actual transportation rate WA of the particulate material under transportation. A similar problem is also encountered when the properties of the particulate material are under variation from lot to lot or when the preset value Ws of the desired transportation rate is changed.